class Solution {
public:
int jumpFloorII(int number) {
if (number == NULL) return NULL;
if (number == 1) return 1;
if (number == 2) return 2;
int res = 2;
for (int i = 2;i<number;i++)
res = res*2;
return res;
}
};
或者直接用位运算一步到位
class Solution {
public:
int jumpFloorII(int number) {
if (number == 0 || number == NULL) return NULL;
return 1 << (--number);
}
};